Set of instruments for the implantation of an acetabular prosthesis

ABSTRACT

A method is for implantation of an acetabular prosthesis. The method may include positioning an acetabular calibration guide at an acetabular cavity of a patient, and positioning an acetabular reference guide at a bone site of the patient separate from the acetabular cavity. The method may include aligning a calibration signal and a reference signal, the calibration and reference signals being respectively associated with the acetabular calibration guide and the acetabular reference guide. The method may include removing the acetabular calibration guide and positioning a tool at the acetabular cavity of the patient, and aligning a control signal and the reference signal for identifying a desired orientation of the tool relative to the acetabular cavity, the control signal being associated with the tool.

RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 14/777,717filed Sep. 16, 2015, which is a 371 of International application No.PCT/IB2014/059715 filed Mar. 13, 2014, which claims priority to ItalianApplication No. MI2013A000405 filed Mar. 18, 2013, each application ishereby incorporated herein in its entirety by reference.

FIELD OF THE INVENTION

The present invention relates to a medical device, and more particularlyto, a set of instruments for the implantation of an acetabularprosthesis.

BACKGROUND

The use of endoprostheses to eliminate pain and restore the function ofthe hip joint, especially in patients suffering from osteoarthritis, isa technique that was developed starting from the second half of the lastcentury and is by now well established in the medical art. In mostcases, where both the acetabular cavity and the femoral head of thepatient are compromised by the pathology, a total arthroprosthesis ofthe hip, also called THR—acronym for total hip replacement—is performed.This operating technique entails the implantation of an acetabularprosthesis in the patient's pelvis on the one hand and, on the otherhand, the resection of the femoral head and replacement thereof with aprosthetic stem endowed with an articulating ball that fits into theaforesaid prosthesis.

Despite having led to some excellent clinical results in terms offunctional recovery of the joint, arthroprosthesis of the hip has somemajor drawbacks. In particular, it has been observed, due to the reduceddiameter of the prosthetic ball, there are frequent episodes ofdisplacement of the artificial joint; not rarely, for the same reason,an arthroprosthesis performed without the necessary precision andexpertise may lead to a disparity in the length of the lower limbs.Finally, arthroprosthesis of the hip does not enable the patient toengage in sports or other stressful activities, making this anunsuitable solution especially for younger patients.

In order to remedy the drawbacks observed in the art, an alternative tothe traditional arthroprosthesis of the hip has been developed in recenttimes, namely, hip resurfacing. This approach involves capping thearticular surface of the pelvis and femoral head with metal cups ofmodest thickness, thereby preserving both the head and neck of thepatient's femur. This operation makes it possible to maintain a jointdiameter that is close to the physiological one, thus reducing the riskof displacements and modifications in the length of the limb.Furthermore, the wear on the components is more limited, with aconsequent lengthening in the average lifespan of the prosthesis.

Both operating approaches summarily described here have in common theneed to prepare the surface of the acetabulum and implant therein anacetabular prosthesis. Preparation entails first of all a step ofcleaning the bone, removing in particular the soft tissues and cartilagewhich preclude correct visualization of the bony landmarks (e.g. theacetabular fossa) present on the periphery of the acetabulum. So-calledacetabular reaming is then performed, using a special tool inserted inthe cavity. Acetabular reaming serves to smooth the internal surface ofthe cavity in order to prepare it to receive the acetabular prosthesis.

Another tool, called an impactor, is used to position and fix theacetabular prosthesis. This tool has a stem, to the end of which thereplacement cotyle is fixed; it enables the prosthetic device both to beinserted in the bone cavity and mechanically locked in place before thestem is withdrawn.

The above-mentioned operations of preparing, positioning and fixing theacetabular prosthesis within the corresponding pelvic cavity areextremely critical and delicate steps in an arthroplasty procedure. Theorientation of the acetabular prosthesis, which is defined by theseoperations, in fact largely determines the implant's success in the longterm. A correct positioning will result in an optimal distribution ofloads and an ideal stability of the prosthesis; an incorrectpositioning, on the contrary, may result in a rapid deterioration of theimplant or in biological complications of another kind.

It should be observed, moreover, that the aforesaid procedures arecomplicated by the difficult access to the bone site, and by the limitedvisibility of the latter. In particular, while in the hiparthroprosthesis operations the removal of the femoral neck serves insome way to make the route toward the acetabulum more pervious, in hipresurfacing arthroplasty the surgeon does not enjoy this relativeadvantage.

It may further be observed that the use of specific guides realized withrapid prototyping systems, currently applied in other orthopaedicsurgical procedures, cannot be easily transferred to operations on theacetabulum. In fact, a vast, easily exposable bone area ensuring astable positioning on the physical guide is lacking around theacetabular cavity.

International patent WO 2011/117644 proposes a set of instruments thatthe surgeon can use to perform operations on the acetabulum, comprising:locating means, temporarily located in the acetabulum; guide means, setin a pre-established position in relation to the locating means andserving as a guide, when in that position, for the instruments used toprepare of the acetabular surface (acetabular reamer) and position andfix the prosthesis (impactor); as well as support means for maintainingthe guide means in that position when the locating means have beenremoved.

SUMMARY

Generally, a method is for implantation of an acetabular prosthesis. Themethod may include positioning an acetabular calibration guide at anacetabular cavity of a patient, and positioning an acetabular referenceguide at a bone site of the patient separate from the acetabular cavity.The method may include aligning a calibration signal and a referencesignal, the calibration and reference signals being respectivelyassociated with the acetabular calibration guide and the acetabularreference guide. The method may include removing the acetabularcalibration guide and positioning at least one tool at the acetabularcavity of the patient, and aligning a control signal and the referencesignal for identifying a desired orientation of the at least one toolrelative to the acetabular cavity, the control signal being associatedwith the at least one tool.

The method may also include reaming the acetabular cavity of the patientafter removing the acetabular calibration guide. The method may compriseproviding a target screen for the aligning of the calibration signal andthe reference signal and the aligning of the control signal and thereference signal. The aligning of the calibration signal and thereference signal and the aligning of the control signal and thereference signal each may comprise aligning signals at a same point onthe target screen. The aligning of the calibration signal and thereference signal and the aligning of the control signal and thereference signal may each comprise aligning respective optical emitterprojections. The aligning of the calibration signal and the referencesignal may be for identifying a desired orientation of the acetabularcalibration guide.

In some embodiments, the acetabular calibration guide may comprise apositioning base configured to mate with the acetabular cavity of thepatient, and the positioning base may include a supporting footconfigured to abut against an internal surface of the acetabular cavity,and a plurality of positioning arms configured to engage with differentpoints on a periphery of the acetabular cavity. The method may alsoinclude inserting a central positioning arm from the plurality ofpositioning arms in an acetabular fossa. The method may also includeabutting a lower positioning arm from the plurality of positioning armsagainst a lower acetabular lip, and abutting an upper positioning armfrom the plurality of positioning arms against an upper acetabular lipof the acetabular cavity.

The method may also include attaching respective optical emitters to theat least one tool, the acetabular calibration guide, and the acetabularreference guide. The method may include creating an incision at theacetabular cavity of the patient and cleaning a bone site of theacetabular cavity of the patient before the positioning of theacetabular calibration guide.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents a perspective view of a first tool and a connectorassociated therewith, belonging to the set of instruments according tothe present invention, the first tool being engaged on a bone site ofthe patient according to one use configuration;

FIG. 2 represents a perspective view of a detail of the first tool inFIG. 1, without the associated connector;

FIG. 3 represents a perspective view of the first tool in FIG. 1, withan optical collimator associated with the connector;

FIG. 4 represents a perspective view of an adaptor belonging to thefirst tool in FIG. 1;

FIG. 5 represents a perspective view of a second tool and an opticalcollimator associated with it by means of a connector, both belonging tothe set of instruments according to the present invention, the secondtool being engaged on a bone site of the patient according to one useconfiguration;

FIG. 6 represents a perspective view of the second tool in FIG. 5,without the associated connector;

FIG. 7 represents a perspective view of an adaptor belonging to thesecond tool in FIG. 5;

FIG. 8 represents a perspective view of an acetabular calibration guide,belonging to the set of instruments according to the present invention,engaged on a bone site of the patient according to one useconfiguration;

FIG. 9 represents a perspective view of a positioning base, belonging tothe acetabular calibration guide in FIG. 8, engaged on a bone site ofthe patient according to one use configuration;

FIG. 10 represents a perspective view of the positioning base in FIG. 9,dissociated from the bone site of the patient;

FIG. 11 represents a perspective view, from a different angle, of thepositioning base in FIG. 10;

FIG. 12 represents a perspective view of a stem belonging to theacetabular calibration guide in FIG. 8;

FIG. 13 represents a perspective view of a detail of the acetabularcalibration guide in FIG. 8, associated by means of a connector to anoptical collimator;

FIG. 14 represents a perspective view of a connector and of a detail ofan acetabular reference guide belonging to the set of instrumentsaccording to the present invention;

FIG. 15 represents a perspective view of a femoral guide belonging tothe set of instruments according to the present invention;

FIG. 16 represents a first step of a surgical method implemented usingthe set of instruments according to the present invention;

FIG. 17 represents a second step of a surgical method implemented bymeans of the set of instruments according to the present invention;

FIG. 18 represents a third step of a surgical method implemented bymeans of the set of instruments according to the present invention.

DETAILED DESCRIPTION

The aforesaid set of instruments, though satisfactory in certainrespects, is clearly very complex in its use. The aforesaid guide meansalso have a considerable bulk, which may hamper the surgeon duringhis/her operation. The technical problem at the basis of the presentinvention is thus to devise set of instruments that enables a correctpositioning of the tools for preparing the acetabular cavity andpositioning an acetabular prosthesis, and which is more compact andsimpler to use than prior art devices.

The aforesaid technical problem is solved by a set of instruments forthe implantation of an acetabular prosthesis, comprising: at least onetool designed to operate in the acetabular cavity of a patient; at leastone emitter, jointly associable with the tool and designed to emit acontrol signal to be aligned with a reference signal that identifies acorrect orientation of the tool relative to the acetabular cavity.

In a preferred embodiment, the emitter includes an optical collimator,for example a laser projector, configured to emit an optical controlsignal, for example a laser beam. The optical control signal can bealigned with a reference optical signal, including, for example, of asecond laser beam, so as to collimate the spots of the two signalsprojected onto a target surface.

It should be noted, moreover, that the possibility of using other priorart technologies for generating and aligning control and referencesignals is not ruled out. For example, such signals could be representedby ultrasound waves that are aligned by equalizing the reflection timesrelative to a target surface.

As may be easily understood by a person skilled in the art, thealignment of the optical collimator with a reference optical signalprovides a simple guide system for the surgical tools used to implantthe acetabular prosthesis, thus defining an advantageous alternative tothe physical guide structures known in the art. By aligning the lightbeam of the collimator with the reference signal, the surgeon can infact control the degree of rotational freedom of a tool whose operatinghead is inserted into the acetabular cavity.

It should be noted that the same inventive idea is applicable, mutatismutandis, to any other technologies for generating and aligning thesignals that might be used. Moreover, it should be noted that theinventive idea can similarly be applied to the various toolssubsequently used to prepare the acetabular cavity and in the subsequentsteps of inserting and fixing the acetabular prosthesis. Such tools mayinclude, for example, an acetabular reamer and/or an impactor for theacetabular prosthesis to be implanted.

It may be noted that the reference signal can be obtained and maintainedwith different methods. If an optical collimator is used to generate anoptical control signal, the corresponding reference optical signal canbe processed, for example, by means of software using images of the bonesite of the patient and projected onto a target surface.

Preferably, however, the reference signal is obtained with a secondemitter, which is jointly associated with a bone structure of thepatient that is not involved in the operation of the surgical tools tobe oriented. The set of instruments thus comprises an acetabularreference guide fixable to a bone site of the patient which is separatefrom the acetabular cavity and with which a second emitter designed toemit the reference signal can be jointly associated. Preferably, thebone site is chosen on the same hip bone that has the acetabular cavity.

In the preferred case of an optical collimator used to generate the(optical) control signal, an optical collimator (for example, a laserprojector) is used in the same way to generate the reference signal. Theabove-mentioned solution has the advantage of providing a referencerelative to the patient's hip bone, so that any movements of the bone donot prejudice the correct calibration of the reference provided.

The set of instruments according to the present invention canadvantageously comprise an acetabular calibration guide that can betransitorily associated with the patient's acetabular cavity accordingto a desired orientation, the acetabular calibration guide being jointlyassociable with an emitter designed to emit a calibration signal whichidentifies the orientation of the acetabular guide itself, the referencesignal being able to be aligned with the calibration signal.

Once again, in the preferred case of an optical collimator used togenerate the (optical) control and reference signals, an opticalcollimator (for example a laser projector) is used in the same way togenerate the calibration signal. The acetabular calibration guide can berepresented, in particular, by a physical structure, preferablyrod-shaped, which is temporarily inserted into the acetabular cavity.Once the desired orientation for the rod-shaped structure has beenreached, the signal emitted by the emitter associated with it enablesthe reference signal provided by the second emitter to be calibrated.Therefore, once the acetabular calibration guide has been removed, theremaining reference guide, jointly implanted in a portion of bone at adistance from the acetabulum, enables the orientation previously assumedby the rod-shaped structure to be exactly replicated.

The acetabular calibration guide can comprise, in particular, apositioning base that precisely mates with the patient's acetabularcavity. This positioning base can be realized, for example, on the basisof tomographic images of the bone site acquired prior to surgery.

The acetabular base enables a specific planned orientation to beimmediately replicated, possibly with the aid of software for thethree-dimensional graphics, in the preoperative phase. The positioningbase can have, in particular, a supporting foot intended to abut againstthe internal surface of the acetabular cavity, and a plurality ofpositioning arms intended to engage with different points on theperiphery of the acetabular cavity.

A central positioning arm can, for example, be intended to be insertedin the acetabular fossa, a lower positioning arm to abut against thelower acetabular lip and an upper positioning arm to abut against theupper acetabular lip of the acetabular cavity. It should be noted thatthe same emitter, including in particular an optical collimator in apreferred embodiment of the present invention, can be alternativelyassociated with different tools (acetabular reamer, impactor) and withthe acetabular calibration guide. The second emitter, associated withthe acetabular reference guide, can also be of a type that is identicalto the first and interchangeable with it.

The emitter is preferably mounted on a connector, configured to besnap-fitted to adaptors integral with the various tools as well as on anadaptor integral with the acetabular calibration guide. The same emittercan thus be used in the subsequent steps of calibrating, reaming andimplanting the acetabular prosthesis, while a setting of the emitterrelative to the connector is maintained unchanged.

The same connector can also be snap fitted to an adaptor integral withthe acetabular reference guide; in this case, as previously suggested,the two emitters with the respective connectors are interchangeable witheach other. The emitters can thus be associated with connectorsconfigured to be fitted to specific adaptors integral with the variouscomponents of the set of instruments. In particular, the emitter ispreferably associated with the connector by means of a pivotable jointin order to facilitate calibration of the reference signal. The emittercan further comprise a locking screw serving to selectively block therotation of the pivotable joint once the desired calibration has beenreached.

The set of instruments according to the present invention comprises thefollowing components, broadly described below: an acetabular reamer 1,individually represented in the appended FIGS. 1-3; an impactor 2,individually represented in the appended FIGS. 5-6; and an acetabularcalibration guide 5, individually represented in the appended FIGS.8-13.

The set of instruments further comprises an acetabular reference guide4, which may be seen in the overall FIGS. 16-18; and at least twoemitters, represented in particular by optical collimators 3, identicalto each other and associable with connectors 6. The set of instrumentscan comprise, finally, a femoral guide 7, individually represented inthe appended FIG. 15.

The components listed above, with the exception of the femoral guide 7,are used in sequence, according to the procedures described below, inorder to implant an acetabular prosthesis 100, which is known in itself,inside the acetabular cavity 101 of the hip bone 102 of a patient. Thefemoral guide 7 is used, on the other hand, to perform the resectionsand drilling operations necessary to implant a prosthestic femoralcomponent cooperating with the acetabular prosthesis 100.

In the preferred embodiment represented here, the acetabular reamer 1comprises a stem 11 having a split form, provided on one end with a head12 for mounting a reamer, and at the opposite end with a lateral Chanatype handle 13. At the point of attachment of the lateral handle 13, anadaptor 10 is fitted over the stem, the adaptor being configured toreceive one of the connectors 6 of the optical collimators 3.

The adaptor 10, individually shown in FIG. 4, comprises a collar-typecoupling composed of two semi-cylindrical portions 14 a; 14 b hingedtogether. The two semi-cylindrical portions 14 a; 14 b are configured toencircle a rectilinear portion of the stem 11 of the acetabular reamer,abutting beneath a shoulder 17. The closure of the collar-type couplingis assured by a fastening screw 15, which passes through lateral flanges16 of the two semi-cylindrical portions 14 a; 14 b. Integral with theattachment collar, there is a wedge-like portion 18 of the adaptor 10,which bears a female coupling 19 intended to enable the snap fitting ofa corresponding male coupling 62 of the connector 6.

In the preferred embodiment represented here, the impactor 2 comprises astem 21 having a split form and provided on one end with a head 22suitable for carrying an acetabular prosthesis 100, and on the oppositeend with a longitudinal handle 23. The stem 21 has an oblique distalportion which follows the longitudinal handle 23, then a longitudinalportion parallel to the handle 23, and, finally, a proximal obliqueportion which ends with the head 22, aligned with the handle 23.

In correspondence of the oblique distal portion 23, an adaptor 20 isfitted over the stem 21, the adaptor being configured to receive one ofthe connectors 6 of the optical collimators 3. The adaptor 20,individually shown in FIG. 7, comprises a forked connector composed oftwo elastic walls 24 a; 24 b connected to a same main body 28. The twoelastic walls 24 a; 24 b are configured to grasp the distal obliqueportion 23 of the impactor 2, abutting below a shoulder 27. The closureof the forked connector is assured by a connecting screw 25, whichpasses through two end flanges 26 formed on the two elastic walls 24 a;24 b.

Opposite the elastic walls 24 a; 24 b, the main body 28 has a femalecoupling 29 intended to enable the snap fitting of a corresponding malecoupling 62 of the connector 6. The acetabular reference guide 4 takesthe form of a supporting frame implantable on the hip bone 102 andintended to support one of the optical collimators 3. It comprises, inparticular, a rectilinear stem 41, which is directly implantable on thepatient's bone and has an adaptor 40 on one end, configured to receiveone of the connectors 6 of the optical collimators 3.

The adaptor 40, represented in FIG. 14 together with the connector 6,comprises in particular a female coupling 49 intended to enable the snapfitting of a corresponding male coupling 62 of the connector 6. Theadaptor 40 also has a release button 48, which enables the release ofthe male coupling 62. The acetabular calibration guide 5 includes asupporting frame transitorily associable with the acetabular cavity 101of the patient according to a desired orientation and intended tosupport one of the optical collimators 3.

The acetabular calibration guide 5 comprises, in particular, anelbow-shaped stem 56, a positioning base 51 mounted on the proximal endof the stem 56 and an adaptor 50, which is configured to receive one ofthe connectors 6 of the optical collimators 3 and mounted on the distalend of the stem 56. The positioning base 51 is configured to mateprecisely with the acetabular cavity 101 of the patient; in order toachieve this purpose, it is preferably designed on the basis oftomographic images acquired prior to surgery.

The positioning base 51 has a supporting foot 52 intended to abutagainst the internal surface of the acetabular cavity 101. In a distalposition relative to the supporting foot 52, at the edge of theacetabular cavity 101, three positioning arms branch off: an upperpositioning arm 53 intended to abut against the upper acetabular lip, acentral positioning arm 54 intended to be inserted into the acetabularfossa 104 and a lower positioning arm 55 intended to abut against thelower acetabular lip.

The upper 53 and lower 55 positioning arms are coplanar and at an anglerelative to each other that can range from 50 to 200 degrees; thecentral positioning arm 54, which lies in a plane that is slightlyproximal relative to that of the other two arms 53; 55, is in anintermediate angular position between them.

It should be noted, moreover, that whereas the upper 53 and lower 55positioning arms have a free T-shaped end, the central arm 54 does nothave an enlarged end. The planar extension of the T-shaped ends followsthe profile of the acetabular lips; it may be observed that the end ofthe lower arm 55 has a greater extension than the corresponding end ofthe upper arm 53.

Above the positioning base 51 there is provided a through hole 57, whichpasses through the supporting foot 52 to permit the insertion of a pinfor temporary fixation to the patient's bone. Above the positioning base51 there is also provided an insertion socket 58 oriented at 45°relative to the extension of the supporting foot 52; the proximal end ofthe elbow-shaped stem 56, shown in detail in FIG. 12, is intended to besnap fitted into the insertion socket 58.

It should be noted that the curvature of the elbow-shaped stem 56 issuch that the proximal portion of the stem is substantially aligned withthe supporting foot 52. The adaptor 50, mounted on the distal end of theelbow-shaped stem 56, comprises in particular a female coupling 59intended to enable the snap fitting of a corresponding male coupling 62of the connector 6.

The connector 6, which may be seen in detail in FIG. 14, has a malecoupling 62 that can be snap fitted into any female coupling 19; 29; 49;59 present on the adaptors 10; 20; 40; 50 described previously. Itshould be noted that the male coupling 62 and the female couplings 19;29; 49; 59 have an eccentric structure so as to preclude the relativerotation of the components associated by means of a snap fit.

It may be noted that the configuration of the instruments and of thecouplings is such that the female couplings 19; 29; 59 respectivelyassociated with the acetabular reamer 1, the impactor 2 and theacetabular calibration guide 5 have an identical position andorientation, in the operative configuration, relative to the acetabularcavity 101.

The connector 6 comprises a main body 63, which has the male coupling 62at one of its ends and a pivotable joint 61 at the opposite end. Thepivotable joint 61 includes in particular a ball pivotably housed in aU-shaped seat of the main body 63. The pivotable ball can be associated,by means of a screw integral with a tightening knob 30, with the opticalcollimator 3, represented in this case by a laser projector with anelongated shape.

Thanks to the pivotable joint 61, it is thus possible to modify theorientation of the laser projector relative to the main body 63 of theconnector 6 which supports it. A locking screw 60 which passes throughthe main body 63 of the connector 6 enables the aforesaid pivotablejoint 61 to be locked in the desired position, so as to fix the positionof the laser projector relative to the main body 63.

The femoral guide 7, which can be part of the set of instrumentsaccording to the present invention, comprises holes 71 a for connectingwith a manual support pin and 71 b for the insertion of a temporaryfixing pin. The surface 72 a represents the cutting surface on which thesurgeon can rest the instrument for resecting the femoral bone 103.Present on the surface 72 a there is a block 72 b for limiting theextent of the cut in order to preserve the greater trochanter.

We shall now go on to describe, with specific reference to the appendedFIGS. 16-18, a surgical method for the implantation of an acetabularprosthesis according to the present invention. In a first step of themethod, following the traditional operations of incision and preliminarycleaning of the bone site, one proceeds to position the acetabularcalibration guide 5.

As previously discussed, the acetabular calibration guide can beassociated with the acetabular cavity 101 of the patient in a preciseposition so as to define a desired orientation for the tools which willbe subsequently used on the same bone site. In this step, the opticalcollimator 3 must be fixed to the acetabular calibration guide 5 bymeans of the connector 6. The optical collimator 3 projects an opticalcalibration signal 32, which serves to define a punctiform spot on ascreen or another target surface 33.

It may be noted in FIG. 16 that the target screen 33 can includes aconcentric target for evaluating the accuracy of alignment of twooptical signals. Again in this step, one proceeds to implant thepreviously defined acetabular reference guide 4 on a portion of thepatient's hip bone 102 at a distance from the acetabular cavity 101. Arespective optical collimator 3 must be associated with this guide, too.The collimator 3 projects a reference optical signal 30, which serves todefine a punctiform spot on the aforesaid target screen 33.

The method then envisages a step of calibrating the reference opticalsignal 31. To calibrate this signal, the punctiform spot defined on thetarget screen is collimated with the one defined by the opticalcalibration signal 32 previously defined, as shown in FIG. 16. Thecalibration can be performed by acting upon the pivotable joint 61 ofthe connector 6 associated with the acetabular reference guide 4.

Only after the reference optical signal 30 has been calibrated, theacetabular calibration guide 5 is extracted so as to disengage theacetabular cavity 101. Subsequently, the acetabular cavity 101 is reamedby means of the acetabular reamer 1, with which the optical collimator 3previously fitted to the acetabular calibration guide 5 is associated.The optical signal projected by the optical collimator 3 now takes on afunction of controlling the orientation of the tool, which is the reasonwhy it will hereinafter be identified as an optical control signal 30.

In this step, the surgeon can use the reference optical signal 31 toorient the tool 1 in the desired direction, that is to say, in thedirection initially assumed by the acetabular calibration guide 5. Toachieve this, as illustrated in FIG. 17, it is sufficient to collimatethe spot of the optical control signal 30 with that of the referenceoptical signal 31.

In fact, the morphological identicalness between the acetabularcalibration guide 5 and acetabular reamer 1 ensures that, in the eventof alignment, the optical control signal 30 will strike in the samepoint as the optical calibration signal 32, previously collimated withthe reference optical signal 31.

In a subsequent step of applying the acetabular prosthesis 100, use ismade of the previously described impactor 2, which is fitted with theoptical collimator 3 previously used in combination with the acetabularcalibration guide 5 and the acetabular reamer 1. In this case as well,as shown in FIG. 18, the surgeon has the possibility of easily aligningthe tool 2 with the chosen spatial reference by collimating thepunctiform spot generated by the optical control signal 30 with the spotdue to the optical calibration signal 31.

It is wholly evident that the main advantage of the set of instrumentsaccording to the present invention lies in its singular structuralsimplicity. The advantage of minimal invasiveness in the surgical areais likewise important.

A further advantage lies in the fact that the surgeon is allowed amplefreedom of action during the operations of preparing the acetabularsurface. In fact, the surgeon can freely perform the preliminaryroughing operations according to his/her personal skill and according tohis/her perception of the circumstances, and then be guided by the laserbeam emitted by the tool only on the occasion of the final finishingoperations, aimed at achieving, with precision, the final shape in theexact position desired.

Obviously, in order to satisfy specific contingent requirements, theperson skilled in the art may introduce numerous modifications andvariants to the above-described set of instruments, all remaining withinthe scope of protection of the invention as defined in the followingclaims.

That which is claimed is:
 1. A method for implantation of an acetabularprosthesis, the method comprising: positioning an acetabular calibrationguide at an acetabular cavity of a patient; positioning an acetabularreference guide at a bone site of the patient separate from theacetabular cavity; aligning a calibration signal and a reference signal,the calibration and reference signals being respectively associated withthe acetabular calibration guide and the acetabular reference guide;removing the acetabular calibration guide and positioning at least onetool at the acetabular cavity of the patient; and aligning a controlsignal and the reference signal for identifying a desired orientation ofthe at least one tool relative to the acetabular cavity, the controlsignal being associated with the at least one tool.
 2. The methodaccording to claim 1 further comprising reaming the acetabular cavity ofthe patient after removing the acetabular calibration guide.
 3. Themethod according to claim 1 further comprising providing a target screenfor the aligning of the calibration signal and the reference signal andthe aligning of the control signal and the reference signal.
 4. Themethod according to claim 3 wherein the aligning of the calibrationsignal and the reference signal and the aligning of the control signaland the reference signal each comprises aligning signals at a same pointon the target screen.
 5. The method according to claim 1 wherein thealigning of the calibration signal and the reference signal and thealigning of the control signal and the reference signal each comprisesaligning respective optical emitter projections.
 6. The method accordingto claim 1 wherein the aligning of the calibration signal and thereference signal is for identifying a desired orientation of theacetabular calibration guide.
 7. The method according to claim 1 whereinthe acetabular calibration guide comprises a positioning base configuredto mate with the acetabular cavity of the patient; and wherein thepositioning base includes a supporting foot configured to abut againstan internal surface of the acetabular cavity, and a plurality ofpositioning arms configured to engage with different points on aperiphery of the acetabular cavity.
 8. The method according to claim 7further comprising inserting a central positioning arm from theplurality of positioning arms in an acetabular fossa.
 9. The methodaccording to claim 7 abutting a lower positioning arm from the pluralityof positioning arms against a lower acetabular lip, and abutting anupper positioning arm from the plurality of positioning arms against anupper acetabular lip of the acetabular cavity.
 10. The method accordingto claim 1 further comprising attaching respective optical emitters tothe at least one tool, the acetabular calibration guide, and theacetabular reference guide.
 11. The method according to claim 1 furthercomprising creating an incision at the acetabular cavity of the patientand cleaning a bone site of the acetabular cavity of the patient beforethe positioning of the acetabular calibration guide.
 12. A method forimplantation of an acetabular prosthesis, the method comprising:positioning an acetabular calibration guide at an acetabular cavity of apatient; positioning an acetabular reference guide at a bone site of thepatient separate from the acetabular cavity; aligning a calibrationsignal and a reference signal, the calibration and reference signalsbeing respectively associated with the acetabular calibration guide andthe acetabular reference guide; removing the acetabular calibrationguide and positioning at least one tool at the acetabular cavity of thepatient; reaming the acetabular cavity of the patient after removing theacetabular calibration guide; and aligning a control signal and thereference signal for identifying a desired orientation of the at leastone tool relative to the acetabular cavity, the control signal beingassociated with the at least one tool; the aligning of the calibrationsignal and the reference signal and the aligning of the control signaland the reference signal each comprising aligning respective opticalemitter projections.
 13. The method according to claim 12 furthercomprising providing a target screen for the aligning of the calibrationsignal and the reference signal and the aligning of the control signaland the reference signal.
 14. The method according to claim 13 whereinthe aligning of the calibration signal and the reference signal and thealigning of the control signal and the reference signal each comprisesaligning signals at a same point on the target screen.
 15. The methodaccording to claim 12 wherein the aligning of the calibration signal andthe reference signal is for identifying a desired orientation of theacetabular calibration guide.
 16. The method according to claim 12wherein the acetabular calibration guide comprises a positioning baseconfigured to mate with the acetabular cavity of the patient; andwherein the positioning base includes a supporting foot configured toabut against an internal surface of the acetabular cavity, and aplurality of positioning arms configured to engage with different pointson a periphery of the acetabular cavity.
 17. The method according toclaim 16 further comprising inserting a central positioning arm from theplurality of positioning arms in an acetabular fossa.
 18. The methodaccording to claim 16 abutting a lower positioning arm from theplurality of positioning arms against a lower acetabular lip, andabutting an upper positioning arm from the plurality of positioning armsagainst an upper acetabular lip of the acetabular cavity.
 19. The methodaccording to claim 12 further comprising attaching respective opticalemitters to the at least one tool, the acetabular calibration guide, andthe acetabular reference guide.
 20. The method according to claim 12further comprising creating an incision at the acetabular cavity of thepatient and cleaning a bone site of the acetabular cavity of the patientbefore the positioning of the acetabular calibration guide.